循环 Java 的类属性?
问题说明
如何在java中动态循环类属性.
How can I loop over a class attributes in java dynamically.
例如:
public class MyClass{
private type1 att1;
private type2 att2;
...
public void function(){
for(var in MyClass.Attributes){
System.out.println(var.class);
}
}
}
这在 Java 中可行吗?
is this possible in Java?
正确答案
没有语言支持来完成您的要求.
There is no linguistic support to do what you're asking for.
您可以在运行时使用反射(例如使用 Class.getDeclaredFields() 获取Field)，但取决于你想要做什么，这可能不是最好的解决方案.
You can reflectively access the members of a type at run-time using reflection (e.g. with Class.getDeclaredFields() to get an array of Field), but depending on what you're trying to do, this may not be the best solution.
这里有一个简单的例子，只展示了反射能够做的一些事情.
Here's a simple example to show only some of what reflection is capable of doing.
import java.lang.reflect.*;
public class DumpFields {
public static void main(String[] args) {
inspect(String.class);
}
static <T> void inspect(Class<T> klazz) {
Field[] fields = klazz.getDeclaredFields();
System.out.printf("%d fields:%n", fields.length);
for (Field field : fields) {
System.out.printf("%s %s %s%n",
Modifier.toString(field.getModifiers()),
field.getType().getSimpleName(),
field.getName()
);
}
}
}
上面的代码片段使用反射来检查class String 的所有声明字段；它产生以下输出:
The above snippet uses reflection to inspect all the declared fields of class String; it produces the following output:
7 fields:
private final char[] value
private final int offset
private final int count
private int hash
private static final long serialVersionUID
private static final ObjectStreamField[] serialPersistentFields
public static final Comparator CASE_INSENSITIVE_ORDER
Effective Java 2nd Edition，Item 53:首选接口而非反射
以下是本书的摘录:
Effective Java 2nd Edition, Item 53: Prefer interfaces to reflection
These are excerpts from the book:
给定一个 Class 对象，可以获取构造函数、方法和Field 实例表示类的构造函数、方法和字段.[它们] 让你反射性操纵它们的底层对应物.然而，这种力量是有代价的:
Given a
Classobject, you can obtainConstructor,Method, andFieldinstances representing the constructors, methods and fields of the class. [They] let you manipulate their underlying counterparts reflectively. This power, however, comes at a price:
- 您失去了编译时检查的所有好处.
- 执行反射访问所需的代码笨拙而冗长.
- 性能受到影响.
通常，在正常应用程序中，不应在运行时反射性地访问对象.
As a rule, objects should not be accessed reflectively in normal applications at runtime.
有一些复杂的应用程序需要反射.示例包括[...故意省略...]如果您对您的应用程序是否属于这些类别之一有任何疑问，它可能不属于.
There are a few sophisticated applications that require reflection. Examples include [...omitted on purpose...] If you have any doubts as to whether your application falls into one of these categories, it probably doesn't.
这篇好文章是转载于：学新通技术网
